UB Engineer Discovers Carbon Composite is A Semiconductor

SAN DIEGO, Calif. -- A University at Buffalo engineer has made the first observation of semiconducting behavior in a carbon composite material, a finding that could revolutionize the fields of "smart" structures and electronics.

The research was presented here today (March 4, 1998) at the International Symposium on Smart Structures and Materials in San Diego.

Chung, who also is Niagara Mohawk Chair of Materials Research at UB, co-authored the paper with Shoukai Wang, a doctoral candidate in the UB Department of Mechanical and Aerospace Engineering.

Made from carbon fibers embedded in a polymer matrix, the new semiconducting material would be easier and less expensive to fabricate than traditional silicon-based electronics. Because it would spread electronic capabilities over a much larger surface area, heat dissipation -- now one of the biggest technological challenges facing electronic packaging -- would no longer be a problem.

Known for their durability and light weight, carbon composites are used primarily to manufacture aircraft parts and are being used increasingly in automotive components, bridges, machinery and sporting equipment.

Currently, optical or electronic sensors for detecting strain and deformation are embedded in carbon composites used to make aircraft parts, a process that itself can weaken significantly the structural component.

"In addition, these devices can only be embedded in certain locations, not throughout the whole component," said Chung.

"With this material, the whole piece is 'smart' and no electrical interconnection is needed," she said.

A structural electronic material also would have exceptional energy-storage potential, she added, allowing an aircraft component to act like a huge solar cell.

It also would make solar cars more feasible because energy could be stored throughout body panels constructed of carbon composites.

The discovery is unusual because it unites advances in two disciplines that typically don't "talk" to each other, Chung explained.

"In the semiconductor world, silicon dominates so completely that people tend not to think about other kinds of materials, especially structural materials," she said. "On the other hand, structural engineers would never think of their materials as semiconductors."

Chung, who is a materials engineer, made the discovery while examining the electrical behavior of carbon composites as a way to improve damage detection. She was focusing on how changes in temperature in composite structures could be sensed using the structural material itself.

She found that the electrical properties of the composite material changed with temperature.

"That variation in temperature is a signature of a semiconductor," she said.

"But what's even more unusual about this particular material is that it is semiconducting in one direction and metallic in another," she said. "Usually, a semiconductor, like silicon, is semiconducting in all directions."

The research shows that the carbon-fiber composite, consisting of layers of carbon fibers, is semiconducting perpendicular to the plane of the junction where the fibers intersect and metallic along its horizontal plane.

The advantage of having both in one material, Chung explained, is that the metal characteristics provide a system of built-in electrical contacts and leads for the composite to which a meter can be connected.

In addition, she said, by using the fibers as a conductor and putting an insulator in between the fiber layers, a large capacitor is formed, so that energy can be stored throughout an aircraft or automotive component made of the composite.

Chung plans to focus on optoelectronic and electronic devices made from the composite.

A patent has been filed on the invention.